The present grant extends the objectives of our recent grant HL-23071-01, entitled "Electrophysiology of Lethal Arrhythmias" (E. Neil Moore, principal investigator). The former grant combines animal investigations and human studies in the Catheterization Laboratory. The human studies deal with and are limited to studies in the Clinical Electrophysiology Laboratory and include three aspects: 1) Mechanism and therapy of recurrent sustained ventricular tachycardia, 2) predictive value of repetitive ventricular responses to programmed stimulation, RV and LV refractory periods and sequence of ventricular activation for sudden death, and 3) relationship of (1) and (2) to coronary and left ventricular anatomy. The present studies deal primarily with intraoperative assessment of activation, recovery and refractoriness and the effects of reperfusion (bypass grafting) on these parameters. Intraoperative assessment of the site of origin and mechanism of ventricular tachycardia will be another goal. Data from this endeavor will provide information to develop new and/or additional surgical techniques to more successfully ablate this arrhythmia. Thus while our grant HL 23071-01 and the present grant application deal with a similar topic, the specific areas of research and goals differ. There is no overlap in funding of the two proposals.